Binding Properties of Antimicrobial Agents to Lipid Membranes Using Surface Plasmon Resonance

Abstract

In the present study, we examined the interaction of antimicrobial agents with four model lipid membranes that mimicked mammalian cell membranes and Gram-positive and -negative bacterial membranes and analyzed the binding kinetics using our surface plasmon resonance (SPR) technique. The selective and specific binding characteristics of antimicrobial agents to the lipid membranes were estimated, and the kinetic parameters were analyzed by application of a two-state reaction model. Reproducible analysis of binding kinetics was observed. Vancomyicn, teicoplanin, erythromycin, and linezolid showed little interaction with the four lipid membranes in the SPR system. On the other hand, vancomycin analogues showed interaction with the model lipid membranes in the SPR system. The selective and specific binding characteristics of vancomycin analogues to the lipid membranes are discussed based on data for in vitro antibacterial activities and our data on the binding affinity of the D-alanyl-D-alanine terminus of a pentapeptide cell wall obtained by SPR. The mechanism of antibacterial activity against Staphylococcus aureus and vancomycin-resistant enterococci could be evaluated using the binding affinity obtained with our SPR techniques. The results indicate that the SPR method could be widely applied to predict binding characteristics, such as selectivity and specificity, of many antimicrobial agents to lipid membranes.

The properties and mechanisms of drug interactions with biological membranes serve as critical information in the drug discovery stage to characterize the pharmacokinetics and pharmacodynamics properties of drug candidates. In particular, the affinity of antimicrobial agents for lipid membranes is one of the critical factors influencing their selectivity and potency and plays an important role in the antimicrobial mechanism of action.^1–7) In order to accelerate drug discovery and development, various in vitro analytical techniques, such as circular dichroism spectroscopy, fluorescence spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and fluorescence resonance energy transfer, have been employed.^8–10)

Recently, surface plasmon resonance (SPR)-based biosensors have been widely used to study the membrane-binding properties of drugs with the aim of gaining insight into their modes of action.^11,12) The use of SPR-based biosensors to study the membrane-binding properties of drugs has the advantage of not requiring the presence of labels or chromophores.¹³⁾ We have already established the evaluation of interactions of various antimicrobial peptides to ligands using SPR biosensors, and demonstrated that the kinetic rate constants and the affinities of ligand interactions can be readily determined by this technique, which in turn provides important insights into the interaction mechanisms.^14–16) Also, our SPR techniques have already been used to evaluate the binding properties of an antimicrobial agent (Daptomycin) and antifungal agents (Amphotericin B and Fungizone) to lipid membranes.^17–19)

Glycopeptide antibiotics are widely used to treat various infections caused by Gram-positive bacteria by inhibiting proper cell wall synthesis, specifically, by binding to the D-alanyl-D-alanine residues on the ends of the peptide chains of the membrane-anchoring cell wall precursor, lipid II.^20–24) On the other hand, vancomycin, a glycopeptide antibiotic, cannot bind to lipid II when the last D-alanine residue has been replaced by a D-lactate (D-alanyl-D-lactate). This substitution leads to vancomycin resistance.^25,26) Recently, we developed a SPR assay to examine the binding properties of glycopeptide antibiotics, including vancomycin, to dipeptide ligands, mimicking vancomycin-susceptible (D-alanyl-D-alanine) and -resistant (D-alanyl-D-lactate) dipeptides of lipid II.²⁷⁾ In our report, we discussed the correlation of SPR data on the interaction of antibiotics with dipeptide ligands and their antibacterial activity against Staphylococcus aureus and vancomycin-resistant enterococci (VRE).²⁷⁾ The interactions of some vancomycin analogs with lipid II did not show good correlation with their antibacterial activities.²⁷⁾ Some glycopeptide antibiotics are known to perturb bacterial cell membrane potential and permeability.^22,28) Therefore, the affinity of antibacterial agents for the lipid membranes was investigated, combining the two data sets on antibacterial activities.

We have demonstrated the interactions of various antimicrobial agents, including glycopeptide antibiotics, with four model lipid membranes which mimicked mammal cell membranes as well as Gram-positive and -negative bacterial membranes using our established SPR techniques, including analysis of the binding kinetics of lipid membranes.^14–16,29) Our final target was to predict the mechanism of the antibacterial activity of antibiotic drugs using the SPR system.

This paper describes an investigation of the lipid membrane-binding properties of antimicrobial agents (vancomycin, its four analogs, teicoplanin, erythromycin, and linezolid) with four model lipid membrane systems using the SPR method. The binding kinetics of antimicrobial agents with model lipid membranes was estimated and good reproducibility was obtained. Vancomycin showed little binding to lipid membranes, but Van-M-02, ΔN-Van-M-02 (vancomycin analogs) and Dimer 1 (vancomycin dimer) could bind to them. The relationship between the interaction of antimicrobial agents to the lipid membranes and the antimicrobial activity is discussed, based on both the data for antibacterial activities in vitro and our reported data on the binding affinity of the D-alanyl-D-alanine terminus of a pentapeptide cell wall by SPR.²⁷⁾ The mechanism of antibacterial activity against Staphylococcus aureus and vancomycin-resistant enterococci could be evaluated using the binding affinity obtained by our SPR techniques. The findings showed that our SPR method could be widely applied as an in vitro system to predict the binding characteristics, such as selectivity and specificity, of many antimicrobial agents to lipid membranes.

MATERIALS AND METHODS

Reagents and Chemicals

Vancomycin synthesized in our laboratories was used. Van-M-02, ΔN-Van-M-02, Dimer 1 and Dimer 2 were synthesized at Tohoku University (Fig. 1). Teicoplanin, erythromycin, linezolid and dimethyl sulfoxide (DMSO) were purchased from Sigma-Aldrich Co., LLC (St Louis, MO, U.S.A.). Distilled water (HPLC grade) was purchased from Nacalai Tesque, Inc. (Kyoto, Japan). 1-Palmitoyl-2-oleoylphosphatidylcholine (POPC), 1-palmitoyl-2-oleoylphosphatidyl-glycerol (POPG), 1-palmitoyl-2-oleoylphosphatidyl-ethanolamine (POPE) and 1,1′,2,2′-tetraoleoyl cardiolipin (CL) were purchased from Avanti Polar Lipids, Inc. (Alabaster, AL, U.S.A.). 3-[(3-Cholamidpropyl)-dimethylammonio] propanesulfonate (CHAPS) and chloroform were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Concentrated phosphate buffered saline (PBS) was purchased from GE Healthcare U.K., Ltd. (Buckinghamshire, England).

Fig. 1. Chemical Structures of Vancomycin, Van-M-02, ΔN-Van-M-02, Dimer 1 and Dimer 2

Apparatus

The SPR system used was a BIACORE 3000 analytical system, and a Sensor Chip L1 was used for immobilization of the liposomes (GE Healthcare U.K., Ltd.). The running buffers used were 2×PBS for immobilization of lipid membranes on the chip, and 2×PBS containing 5% DMSO to estimate the interaction of antimicrobial agents with the membrane. As washing solutions to remove the liposome from the Sensor Chip L1, 2-propanol/50 mmol/L sodium hydroxide (1 : 1, v/v) and 20 mmol/L CHAPS were used. The regeneration solution was 50 mmol/L sodium hydroxide. All solutions were freshly prepared, degassed and filtered through a 0.22 µm filter.

Liposome Preparation

In order to prepare individual stock solutions, dry POPC, POPG, POPE and CL were dissolved in chloroform. These stock solutions were prepared at the desired ratios: POPC, POPG, POPG/CL (1 : 1, v/v) and POPE/POPG (4 : 1, v/v). The solvents were evaporated under a stream of nitrogen, and the lipids were dried under centrifuged evaporation. The lipids were resuspended in 2×PBS at approximately 25°C. The resulting lipid dispersion (1 mmol/L POPC, POPG, POPG/CL (1 : 1, v/v) and POPE/POPG (4 : 1, v/v)) was sonicated until it was nearly clear, and extruded 21 times through polycarbonate filters to obtain small unilamellar vesicles (SUV) of 100 nm in size (LiposoFast, pore diameter 100 nm). The extruded lipid dispersion was diluted twofold with 2×PBS containing 300 mmol/L sodium chloride (0.5 mmol/L with respect to phospholipid for POPC, POPG, POPG/CL (1 : 1, v/v) and POPE/POPG (4 : 1, v/v)).

Formation of Lipid Bilayer Membranes

The Sensor Chip L1 surface was washed with injections of 5 µL of 2-propanol/50 mmol/L sodium hydroxide (1 : 1, v/v) and 20 mmol/L CHAPS at a flow rate of 5 µL/min. SUVs (80 µL) were immediately applied to the sensor chip at a flow rate of 2 µL/min for liposome capture. To remove any multilamellar structures from the lipid surface, 30 µL of 50 mmol/L sodium hydroxide was injected at a flow rate of 50 µL/min, which resulted in a stable baseline corresponding to the supported lipid bilayer.²⁹⁾

Antimicrobial Agent Binding to the Bilayer Membrane

Antimicrobial agent assay solutions were prepared by being dissolved in 2×PBS containing 5% DMSO from 20 to 50 µmol/L (20, 25, 30, 35, 40, 45 and 50 µmol/L). The antimicrobial agent solution (50 µL, 100 s) was injected over the lipid surface at a flow rate of 30 µL/min so as to avoid any limitation by mass transfer. Upon completion of injection, the buffer flow was continued to allow a dissociation time of 700 s. All binding experiments were carried out at 25°C. To remove the antimicrobial agent bound to liposome after dissociation, 10 µL of 50 mmol/L sodium hydroxide as regeneration solvent was injected at a flow rate of 30 µL/min before the next injection of antimicrobial agent over the sensor chip. The affinity of the antimicrobial agent for the lipid bilayer membrane was determined by analysis of a series of response curves collected at seven different antimicrobial agent concentrations injected over each lipid surface in triplicate under the condition of 2×PBS containing 5% DMSO as a running buffer.

Data Analysis

The sensorgrams for each antimicrobial–lipid interaction were analyzed by curve fitting using numerical integration analysis (20–50 µmol/L). The data were fitted globally by simultaneously fitting the antimicrobial agent sensorgrams obtained at seven different concentrations using BIA evaluation software (Ver 4.1). The two-state reaction model was applied to the antimicrobial agent binding curves to estimate the association and dissociation rate constants. We chose this model on the basis of results from previous studies on antimicrobial–membrane interactions, in order to estimate the potency of antimicrobial activity induced by disruption of the bacterial membrane of the agents.^14,17–19) This model describes two steps, which in terms of the antimicrobial–lipid interaction, would correspond to:

  

Here A is an antimicrobial, L is the lipid membrane, AL is the initial complex formed by the lipid membrane and the antimicrobial via, for example, an electrostatic interaction. The complex AL changes to AL*, which cannot dissociate directly to A+L, and which may correspond to the insertion of an antimicrobial agent into the lipid bilayer.

The corresponding differential rate equations for this reaction model have been reported.^30–35) The association (k_a1, k_a2) and dissociation (k_d1, k_d2) rate constants and the affinity constant (K) estimated by the two-state reaction model are represented by

  

RESULTS AND DISCUSSION

Kinetic Parameters and Sensorgrams of Antimicrobial Agents for the Model Lipid Membranes

In this SPR study, four different liposome mixtures were used as model lipid systems. POPC was used to mimic mammalian membranes, while POPG and POPG/CL (1 : 1, v/v) were used as Gram-positive membrane systems.^17,29,36) POPE/POPG (4 : 1, v/v) was used as a negative bacterial membrane system.^17,29) The response units of lipid membranes immobilized on the L1 chip were confirmed to be approximately 5000–10000 as the same levels.¹⁷⁾

Various vancomycin analogs have been synthesized and their antimicrobial activities have been estimated and characterized.^37–40) Van-M-02 (Fig. 1), synthesized as a glycopeptide inhibitor of peptidoglycan synthesis, has activities against Gram-positive bacteria including VRE. ΔN-Van-M-02 (Fig. 1), N-terminal-degraded Van-M-02 was synthesized in order to assess the contribution of the D-alanyl-D-alanine binding pocket to the activity of Van-M-02.³⁷⁾ Dimer 1 and Dimer 2 (Fig. 1) synthesized as vancomycin dimers exhibit strong activity against vancomycin-resistant bacteria.^38–40)

Representative sensorgrams presented in Fig. 2 showed few interactions of vancomycin, Dimer 2, teicoplanin, erythromycin and linezolid with the POPC, POPG, POPG/CL (1 : 1, v/v) and POPE/POPG (4 : 1, v/v) liposome membranes immobilized on the Sensor Chip L1 using 2×PBS containing 5% DMSO as a running buffer. Few responses were obtained on calculation of the parameters of the two-state reaction model. On the other hand, Fig. 3 showing representative sensorgrams of the binding of Van-M-02, ΔN-Van-M-02 and Dimer 1 taken under the same conditions, revealed a distinct increase in the response to higher antimicrobial agent concentrations, indicating that the system had not reached saturation.

Fig. 2. Sensorgrams for Vancomycin, Dimer 2, Teicoplanin, Erythromycin and Linezolid of Binding to Liposome Membranes Immobilized on the Sensor Chip L1 Surface (1, POPC; 2, POPG; 3, POPG/CL (1 : 1, v/v); 4, POPE/POPG (4 : 1, v/v))

Running buffer, 2×PBS containing 5% DMSO (each compound concentration=50 µmol/L).

Fig. 3. Sensorgrams for Van-M-02, ΔN-Van-M-02 and Dimer 1 of Binding to Liposome Membranes Immobilized on the Sensor Chip L1 Surface

Running buffer, 2×PBS containing 5% DMSO (each compound concentration=20–50 µmol/L).

The association (k_a1, k_a2) and dissociation (k_d1, k_d2) rate constants and the affinity constant (K) of vancomycin and its four analogs estimated by the two-state reaction model are listed in Table 1. The reproducibility of each parameter by repeated assay was good. This model was selected based on the multistep model of antimicrobial–lipid interactions, which may involve an initial binding interaction between the antimicrobial and the head group of the liposome (step 1, characterized by k_a1, k_d1), including an electrostatic interaction, and followed by a reorientation and/or insertion of the analyte into the hydrophobic interior (step 2, characterized by k_a2, k_d2), based on the antimicrobial–membrane interaction.^14,17–19) In this model, the values of k_a1/k_d1 and k_a2/k_d2 correspond to the affinity constants for the initial binding interaction, including the electrostatic and hydrophobic interactions between an antimicrobial and a lipid.

Table 1. Association (k_a1 and k_a2), Dissociation (k_d1 and k_d2) Rate Constants and Affinity Constant (K) Determined by Numerical Integration Using theTwo-State Reaction Model (n=3)

Compound	Lipid type	ka1 (1/Ms)	kd1 (×10−2, 1/s)	ka2 (×10−4, 1/s)	kd2 (×10−5. 1/s)	K (×103, 1/M)
Vancomycin	POPC	—c)	—	—	—	—
	POPG	—	—	—	—	—
	POPG/CLa)	—	—	—	—	—
	POPE/POPGb)	—	—	—	—	—
Van-M-02	POPC	197±96.7d)	10.1±0.805	4.59±1.00	94.2±31.4	3.00±1.30
	POPG	977±108	3.28±0.0854	1.88±0.999	50.1±13.8	41.3±7.65
	POPG/CL	1220±122	2.55±0.0231	3.18±0.661	241±62.9	54.4±4.31
	POPE/POPG	176±41.6	5.95±0.286	7.29±2.09	363±29.4	3.53±0.655
ΔN-Van-M-02	POPC	424±156	7.45±0.544	11.0±2.82	58.4±20.6	20.9±17.9
	POPG	453±64.0	3.41±0.122	2.85±0.401	213±101	15.6±3.42
	POPG/CL	601±60.1	3.19±0.230	4.70±1.13	351±209	22.1±4.76
	POPE/POPG	140±57.9	5.00±0.131	6.20±0.321	211±37.5	3.60±1.33
Dimer 1	POPC	1400±221	1.68±0.0289	19.2±0.200	163±18.8	181±18.9
	POPG	611±101	2.19±0.0231	15.0±0.473	236±20.8	45.6±5.52
	POPG/CL	875±17.3	1.12±0.0100	3.72±0.918	32.9±4.78	171±39.4
	POPE/POPG	1630±123	1.28±0.220	34.8±7.09	255±62.2	308±29.2
Dimer 2	POPC	—	—	—	—	—
	POPG	—	—	—	—	—
	POPG/CL	—	—	—	—	—
	POPE/POPG	—	—	—	—	—

a) POPG/CL (1 : 1, v/v), b) POPE/POPG (4 : 1, v/v), c) Not calculated, d) Mean±standard deviation (n=3).

Binding Properties of Vancomycin and Its Analogs to the Model Lipid Membranes

The results of the kinetic analysis repeatedly showed a higher affinity constant of Van-M-02 for POPG and POPG/CL (1 : 1, v/v), which mimicked Gram-positive bacterial membranes, than POPC and POPE/PG (4 : 1, v/v), which mimicked mammalian membrane and Gram-negative bacterial membranes. This difference in affinity for lipid membranes is likely to depend mainly on the difference in the association (k_a1) rate constant of the first step. The affinity constants of ΔN-Van-M-02 for POPG and POPG/CL (1 : 1, v/v) were higher than that of POPE/PG (4 : 1, v/v), however, the affinity constants of ΔN-Van-M-02 for POPG and POPG/CL (1 : 1, v/v) were similar to that of ΔN-Van-M-02 for POPC.

The affinities of Van-M-02 and ΔN-Van-M-02 for the POPE/PG (4 : 1, v/v) membrane were observed in this SPR system; they were much lower than those of POPG and POPG/CL (1 : 1, v/v) membranes. As these vancomycin analogs were known to not show activity against Gram-negative bacteria, we speculated that the affinities of these vancomycin analogs for the POPE/PG (4 : 1, v/v) membrane would not be caused by the force of their antimicrobial activity against Gram-negative bacteria.

The affinity constants of vancomycin Dimer 1 for all the lipid membranes were greater than those of Van-M-02 and ΔN-Van-M-02. Also, the affinities of Dimer 1 for all the dipeptide terminal of lipid II ligands (including the L-alanyl-L-alanine and the control ligands) were much stronger than those of Van-M-02 and ΔN-Van-M-02.²⁷⁾ The hydrophobic interaction of Dimer 1 with the lipid membranes and dipeptide terminal of lipid II ligands might be stronger than that of Van-M-02 and ΔN-Van-M-02. On the other hand, vancomycin Dimer 2 showed no interactions with any of the model lipid membranes. The reason for this difference may be due to the difference in linker chemical structures between Dimer 1 and Dimer 2.

The affinities of vancomycin analogs to the lipid membranes were compared with data on antibacterial activity and affinity data for lipid II ligands (D-alanyl-D-alanine and D-alanyl-D-lactate ligands).²⁷⁾ Van-M-02 had stronger activity against S. aureus RN4220, E. faecium SR7940 and SR23598, which are VREs with different phenotypes (VanA and VanB, respectively).²⁷⁾ Strong K values of Van-M-02 to POPG and POPG/CL (1 : 1, v/v), which mimicked Gram-positive bacterial membranes, were observed and the affinities of Van-M-02 for D-alanyl-D-alanine and D-alanyl-D-lactate ligands were also stronger than those of vancomycin. This might suggest that the strong antimicrobial activity of Van-M-02 could be attributed to high affinity not only for lipid II but also for lipid membrane.^22,28)

The minimum inhibitory concentration (MIC) value of ΔN-Van-M-02 for S. aureus RN4220 was similar to that of vancomycin, and ΔN-Van-M-02 showed stronger activity against E. faecium SR7940 and SR23598 than those of vancomycin.²⁷⁾ On the other hand, the affinity of ΔN-Van-M-02 to D-alanyl-D-alanine was weaker than that of vancomycin as ΔN-Van-M-02 does not have the N-terminal group which contributes to the D-alanyl-D-alanine binding pocket.²⁷⁾ The higher affinities of ΔN-Van-M-02 for the POPG and POPG/CL lipid membranes than those of vancomycin would lead to higher antimicrobial activity against vancomycin-susceptible and -resistant bacteria than vancomycin. This might suggest that the antimicrobial activity of ΔN-Van-M-02 could be attributed to its affinity for the lipid membrane.

Recently developed glycopeptide antibiotics show antimicrobial activity against vancomycin-resistant bacteria by interaction with other targets (lipid membrane, membrane protein (e.g., penicillin-binding protein 2) and cell-wall peptidoglycan), in addition to affinity for the D-alanyl-D-lactate residue.^41,42) In the present study, we found that Van-M-02 and ΔN-Van-M-02 showed antibacterial activities by interaction with the lipid membrane of vancomycin-resistant bacteria.

Binding Properties of Other Antimicrobial Agents to the Model Lipid Membranes

Teicoplanin, a glycopeptide antibiotic, is known to bind to D-alanyl-D-alanine and D-alanyl-D-lactate residues on the end of the peptide chains of lipid II, and inhibit proper cell wall synthesis in Gram-positive bacteria including some VREs.^43,44) The interaction of teicoplanin with the dipeptide ligands was confirmed in the previous SPR study on the basis of the therapeutic mechanism.²⁷⁾ We speculated that the binding of teicoplanin to the model lipid membranes would not contribute much to the antibacterial activity.

Erythromycin is a macrolide antibiotic that has a wide antimicrobial spectrum and linezolid is an oxazolidinone antimicrobial, which has been approved for the treatment of infections caused by various Gram-positive bacteria, including methicillin-resistant S. aureus and VRE.⁴⁵⁾ These agents bind to ribosome, and inhibit protein synthesis by their effect on the ribosome function.⁴⁶⁾ As we found no binding of erythromycin and linezolid to the model lipid membranes and the dipeptide ligands,²⁷⁾ we speculated that this would affect their therapeutic mechanisms.

CONCLUSION

We examined the interaction of antimicrobial agents with four model lipid membranes that mimicked mammal cell membranes and Gram-positive and negative bacterial membranes and analyzed the binding kinetics by SPR. The selective and specific binding characteristics of the antimicrobial agents to the lipid membranes were estimated and the kinetics parameters were analyzed; reproducible analysis of binding kinetics was observed. As vancomycin and teicoplanin showed less interaction with the four lipid membranes in the SPR system, we speculate that the low affinity of these antimicrobial agents could be attributed to the therapeutic mechanism in vivo for bactericidal activity differing from that of disruption of the bacterial cell membrane. The vancomycin analogs used in this study showed interaction with the model lipid membranes in the SPR system. Vancomycin showed little binding to the lipid membranes, but Van-M-02, ΔN-Van-M-02 and Dimer 1 could bind to them. The selective and specific binding characteristics of vancomycin analogs to the lipid membranes could be clarified by combining data on antibacterial activities in vitro and the data we reported on the binding affinity of the D-alanyl-D-alanine terminus of a pentapeptide cell wall by SPR. Furthermore, the mechanism of antibacterial activity against Staphylococcus aureus and vancomycin-resistant enterococci could be evaluated using the binding affinity obtained by our SPR techniques. The results indicated that the SPR method could be widely applied for predicting binding characteristics, such as selectivity and specificity, of many antimicrobial agents to the lipid membranes as an in vitro system.

REFERENCES

• 1) Silverman JA, Perlmutter NG, Shapiro HM. Correlation of daptomycin bactericidal activity and membrane depolarization in Staphylococcus aureus. Antimicrob. Agents Chemother., 47, 2538–2544 (2003).
• 2) Straus SK, Hancock REW. Mode of action of the new antibiotic for Gram-positive pathogens daptomycin: Comparison with cationic antimicrobial peptides and lipopeptides. Biochim. Biophys. Acta, 1758, 1215–1223 (2006).
• 3) Robbel L, Marahiel MA. Daptomycin, a bacterial lipopeptide synthesized by a nonribosomal machinery. J. Biol. Chem., 285, 27501–27508 (2010).
• 4) Ripoll DR, Liwo A, Scheraga HA. New developments of the electrostatically driven monte carlo method: Test on the membrane-bound portion of melittin. Biopolymers, 46, 117–126 (1998).
• 5) Dempsey CE. The actions of melittin on membranes. Biochim. Biophys. Acta, 1031, 143–161 (1990).
• 6) Ruhr E, Sahl HG. Mode of action of the peptide antibiotic nisin and influence on the membrane potential of whole cells and on cytoplasmic and artificial membrane vesicles. Antimicrob. Agents Chemother., 27, 841–845 (1985).
• 7) Winkowski K, Ludescher RD, Montville TJ. Physiochemical characterization of the nisin–membrane interaction with liposomes derived from Listeria monocytogenes. Appl. Environ. Microbiol., 62, 323–327 (1996).
• 8) Lakey JH, Ptak M. Fluorescence indicates a calcium-dependent interaction between the lipopeptide antibiotic LY146032 and phospholipid membranes. Biochemistry, 27, 4639–4645 (1988).
• 9) Jung D, Rozek A, Okon M, Hancock REW. Structural transitions as determinants of the action of the calcium-dependent antibiotic daptomycin. Chem. Biol., 11, 949–957 (2004).
• 10) Jung D, Powers JP, Straus SK, Hancock REW. Lipid-specific binding of the calcium-dependent antibiotic daptomycin leads to changes in lipid polymorphism of model membranes. Chem. Phys. Lipids, 154, 120–128 (2008).
• 11) Abdiche YN, Myszka DG. Probing the mechanism of drug/lipid membrane interactions using Biacore. Anal. Biochem., 328, 233–243 (2004).
• 12) Baird CL, Courtenay ES, Myszka DG. Surface plasmon resonance characterization of drug/liposome interactions. Anal. Biochem., 310, 93–99 (2002).
• 13) Hall K, Mozsolits H, Aguilar MI. Surface plasmon resonance analysis of antimicrobial peptide–membrane interactions: affinity & mechanism of action. Lett. Pept. Sci., 10, 475–485 (2003).
• 14) Kamimori H, Blazyk J, Aguilar MI. Lipid membrane-binding properties of tryptophan analogues of linear amphipathic β-sheet cationic antimicrobial peptides using surface plasmon resonance. Biol. Pharm. Bull., 28, 148–150 (2005).
• 15) Kamimori H, Unabia S, Thomas WG, Aguilar MI. Evaluation of the membrane-binding properties of the proximal region of the angiotensin II receptor (AT 1A) carboxyl terminus by surface plasmon resonance. Anal. Sci., 21, 171–174 (2005).
• 16) Lerch M, Kamimori H, Folkers G, Aguilar MI, Beck-Sickinger AG, Zerbe O. Strongly altered receptor binding properties in PP and NPY chimeras are accompanied by changes in structure and membrane binding. Biochemistry, 44, 9255–9264 (2005).
• 17) Kinouchi H, Onishi M, Kamimori H. Lipid membrane-binding properties of daptomycin using surface plasmon resonance. Anal. Sci., 29, 297–301 (2013).
• 18) Onishi M, Kamimori H. High-throughput and sensitive assay for amphotericin B interaction with lipid membrane on the model membrane systems by surface plasmon resonance. Biol. Pharm. Bull., 36, 658–663 (2013).
• 19) Oka M, Kamimori H. Lipid membrane-binding properties of amphotericin B deoxycholate (fungizone) using surface plasmon resonance. Anal. Sci., 29, 697–702 (2013).
• 20) Mainardi JL, Villet R, Bugg TD, Mayer C, Arthur M. Evolution of peptidoglycan biosynthesis under the selective pressure of antibiotics in Gram-positive bacteria. FEMS Microbiol. Rev., 32, 386–408 (2008).
• 21) Walsh C. Microbiology: Deconstructing vancomycin. Science, 284, 442–443 (1999).
• 22) Higgins DL, Chang R, Debabov DV, Leung J, Wu T, Krause KM, Sandvik E, Hubbard JM, Kaniga K, Schmidt DE Jr, Gao Q, Cass RT, Karr DE, Benton BM, Humphrey PP. Telavancin, a multifunctional lipoglycopeptide, disrupts both cell wall synthesis and cell membrane integrity in methicillin-resistant Staphylococcus aureus. Antimicrob. Agents Chemother., 49, 1127–1134 (2005).
• 23) Bugg TDH, Dutka-Malen S, Arthur M, Courvalin P, Walsh CT. Identification of vancomycin resistance protein VanA as a D-alanine; D-alanine ligase of altered substrate specificity. Biochemistry, 30, 2017–2021 (1991).
• 24) Koteva K, Hong HJ, Wang XD, Nazi I, Hughes D, Naldrett MJ, Buttner MJ, Wright GD. A vancomycin photoprobe identifies the histidine kinase VanSsc as a vancomycin receptor. Nat. Chem. Biol., 6, 327–329 (2010).
• 25) Xing B, Jiang T, Bi W, Yang Y, Li L, Ma M, Chang CK, Xu B, Yeow EKL. Multifunctional divalent vancomycin: the fluorescent imaging and photodynamic antimicrobial properties for drug resistant bacteria. Chem. Commun. (Camb.), 47, 1601–1603 (2011).
• 26) Xing B, Yu CW, Ho PL, Chow KH, Cheung T, Gu H, Cai Z, Xu B. Multivalent antibiotics via metal complexes: potent divalent vancomycins against vancomycin-resistant enterococci. J. Med. Chem., 46, 4904–4909 (2003).
• 27) Kinouchi H, Arimoto H, Nishiguchi K, Oka M, Maki H, Kitagawa H, Kamimori H. Binding properties of antimicrobial agents to dipeptide terminal of lipid II using surface plasmon resonance. Anal. Biochem., 452, 67–75 (2014).
• 28) Belley A, Neesham-Grenon E, McKay G, Arhin FF, Harris R, Beveridge T, Parr TR Jr, Moeck G. Oritavancin kills stationary-phase and biofilm Staphylococcus aureus cells in vitro. Antimicrob. Agents Chemother., 53, 918–925 (2009).
• 29) Kamimori H, Hall K, Craik DJ, Aguilar MI. Studies on the membrane interactions of the cyclotides kalata B1 and kalata B6 on model membrane systems by surface plasmon resonance. Anal. Biochem., 337, 149–153 (2005).
• 30) Karlsson R, Falt A. Experimental design for kinetic analysis of protein–protein interactions with surface plasmon resonance biosensors. J. Immunol. Methods, 200, 121–133 (1997).
• 31) Morton TA, Myszka DG, Chaiken IM. Interpreting complex binding kinetics from optical biosensors: a comparison of analysis by linearization, the integrated rate equation, and numerical integration. Anal. Biochem., 227, 176–185 (1995).
• 32) Mozsolits H, Wirth HJ, Werkmeister J, Aguilar MI. Analysis of antimicrobial peptide interactions with hybrid bilayer membrane systems using surface plasmon resonance. Biochim. Biophys. Acta, 1512, 64–76 (2001).
• 33) Lee TH, Mozsolits H, Aguilar MI. Measurement of the affinity of melittin for zwitterionic and anionic membranes using immobilized lipid biosensors. J. Pept. Res., 58, 464–476 (2001).
• 34) Mozsolits H, Lee TH, Clayton AHA, Sawyer WH, Aguilar MI. The membrane-binding properties of a class A amphipathic peptide. Eur. Biophys. J., 33, 98–108 (2004).
• 35) Mozsolits H, Unabia S, Ahmad A, Morton CJ, Thomas WG, Aguilar MI. Electrostatic and hydrophobic forces tether the proximal region of the angiotensin II receptor (AT_1A) carboxyl terminus to anionic lipids. Biochemistry, 41, 7830–7840 (2002).
• 36) Epand RF, Savage PB, Epand RM. Bacterial lipid composition and the antimicrobial efficacy of cationic steroid compounds (Ceragenins). Biochim. Biophys. Acta, 1768, 2500–2509 (2007).
• 37) Miura K, Yamashiro H, Uotani K, Kojima S, Yutsudo T, Lu J, Yoshida O, Yamano Y, Maki H, Arimoto H. Mode of action of Van-M-02, a novel glycopeptide inhibitor of peptidoglycan synthesis, in vancomycin-resistant bacteria. Antimicrob. Agents Chemother., 54, 960–962 (2010).
• 38) Nakamura J, Yamashiro H, Hayashi S, Yamamoto M, Miura K, Xu S, Doi T, Maki H, Yoshida O, Arimoto H. Elucidation of the active conformation of vancomycin dimers with antibacterial activity against vancomycin-resistant bacteria. Chemistry, 18, 12681–12689 (2012).
• 39) Lu J, Yoshida O, Hayashi S, Arimoto H. Synthesis of rigidly-linked vancomycin dimers and their in vivo efficacy against resistant bacteria. Chem. Commun. (Camb.), 2007, 251–253 (2007).
• 40) Yoshida O, Nakamura J, Yamashiro H, Miura K, Hayashi S, Umetsu K, Xu S, Maki H, Arimoto H. New insight into the mode of action of vancomycin dimers in bacterial cell wall synthesis. Med. Chem. Commun., 2, 278–282 (2011).
• 41) Kim SJ, Tanaka KSE, Dietrich E, Rafai Far A, Schaefer J. Locations of the hydrophobic side chains of lipoglycopeptides bound to the peptidoglycan of Staphylococcus aureus. Biochemistry, 52, 3405–3414 (2013).
• 42) Nakamura J, Yamashiro H, Miya H, Nishiguchi K, Maki H, Arimoto H. Staphylococcus aureus penicillin-binding protein 2 can use depsi-lipid II derived from vancomycin-resistant strains for cell wall synthesis. Chemistry, 19, 12104–12112 (2013).
• 43) Leclercq R, Courvalin P. Resistance to glycopeptides in enterococci. Clin. Infect. Dis., 24, 545–554, quiz, 555–556 (1997).
• 44) Song JH, Ko KS, Suh JY, Oh WS, Kang CI, Chung DR, Peck KR, Lee NY, Lee WG. Clinical implications of vancomycin-resistant Enterococcus faecium (VRE) with VanD phenotype and vanA genotype. J. Antimicrob. Chemother., 61, 838–844 (2008).
• 45) Tsiodras S, Gold HS, Sakoulas G, Eliopoulos GM, Wennersten C, Venkataraman L, Moellering RC Jr, Ferraro MJ. Linezolid resistance in a clinical isolate of Staphylococcus aureus. Lancet, 358, 207–208 (2001).
• 46) Weisblum B. Erythromycin resistance by ribosome modification. Antimicrob. Agents Chemother., 39, 577–585 (1995).